(1) Field of the Invention
This invention relates to a method of igniting arcs which is suitable for use in producing an electric discharge between at least one main discharging electrode and a workpiece or another electrode to perform, by the heat generated by the electric discharge, a welding, cutting, metallization or heating operation on the workpiece.
(2) Description of the Prior Art
Heretofore, several methods have been available to produce an arc discharge. One of such methods is a high-frequency arc igniting method wherein a high-frequency high voltage is impressed between a main discharging electrode and a workpiece or another electrode to produce an arc discharge between them by causing a dielectric breakdown to occur. Another method is a contact arc igniting method wherein a main discharging electrode is brought into contact with a workpiece to produce a spark by contact and then the main discharging electrode is moved away from the workpiece to convert the spark discharge caused by contact into an arc discharge which is used for performing a desired operation on the workpiece.
Some problems are encountered in these methods of the prior art. In the high-frequency arc igniting method, the high-frequency voltage used for producing an arc is so high that an electromagnetic noise of high magnitude is produced, with a result that a microcomputer or other peripheral electronic devices incorporated in an automatic welding machine might misoperate or suffer damage. This has made it necessary to use a special noise filter to cope with the high frequency noise of high magnitude. Also, measuring equipment coupled to the arc generating circuit might suffer damage when an arc is ignited by using a high-frequency high voltage, making it impossible to readily couple the measuring equipment to the welding electric circuit. Particularly when an alternating current is used for performing welding, it is necessary to impress a high-frequency high voltage to reignite an arc for each A.C. half-wave, so that the incidence of production of a high-frequency noise of high magnitude is high.
In the contact arc igniting method, one may fail in igniting an arc depending on the shape of the forward end of the main discharging electrode and the condition of the surface of the workpiece. When welding is performed by using an alternating current, the stability of the arc may be impaired due to arc extinction which might occur when one half-wave of A.C. is switched to the other half-wave. Reigniting an arc for each half-wave of A.C. is impossible to perform by the contact arc igniting method.